The field of the present invention is that of rocker arm assemblies for internal combustion engines. More particularly, the field of the present invention is that of rocker arm assemblies for internal combustion engines which can be selectively switched between different states of activation of valve operation.
Rocker arms transmit motion from a rotating cam shaft to a stem of a poppet valve to open and close the valve. Almost universally, the valve is spring-biased shut and the cam via the rocker arm controls the opening and closing of the valve. One type of rocker arm is the finger-follower rocker arm.
In recent times, finger-follower and other types of rocker arms have been made to selectively totally or partially deactivate to allow enhanced control of vehicle engines in regard to emissions and fuel economy. In one such rocker arm assembly, the rocker arm has an outer body that engages the valve stem and an inner lost motion arm pivotally mounted on and within the outer body for movement relative to the outer body. The lost motion arm is spring biased upward against an overhead engine cam center lobe to be pivoted by the same. A latch mechanism with an extendable plunger is positioned within the outer body. The plunger is normally in a first position to limit movement of the lost motion arm relative to the outer body so that the cam lobe can pivot the outer body and lost motion arm together as an integral unit to activate the valve stem. Withdrawal of the latch mechanism plunger to a second position allows the lost motion arm to freewheel in a lost motion manner. When the latch mechanism plunger is in the second position the cam may cause the valve to be totally deactivated as described in U.S. Pat. No. 5,653,198 Diggs, issued Aug. 5, 1997. The placement of the latch mechanism plunger in the second position can also cause a low lift or partial deactivation of the valve as provided in U.S. Pat. No. 5,960,755 Diggs, et al. issued Oct. 5, 1999.
A spring biases the plunger in its aforementioned second position. To hold the latch mechanism plunger in the first position for normal operation of the engine there is provided an activating system. The activating system includes an axle or shaft rotatable by a solenoid. An activating arm is disposed about and extends radially from the shaft to engage or disengage the latch mechanism plunger in the first or second position. The activating arm has a contact surface which mates and contacts with the cylindrical surface of a latch pin which is physically connected to the latch mechanism plunger. The activating arm is urged into engagement with the latch pin by a helical coil spring disposed about the activator shaft. Typically in normal conditions the activating arm pushes against the spring which biases the latch mechanism plunger to the second position and thereby maintains the latch mechanism plunger in the aforementioned normal first position. When it is desirable for the latch mechanism plunger to move to its second (disabled or partially disabled position) an engine control unit will supply power to the activator solenoid to cause the activating arm to rotate away from the latch pin to allow the spring to move the latch mechanism plunger to its second position. The aforementioned activating system explained in further detail in Diggs, et al. U.S. patent application Ser. No. 09/731,371 is advantageous over a hydraulically activated system in its speed of response. However the Diggs, et al. rocker arm assembly having the aforementioned activating system is most conducive to a line of rocker arms on a common engine block bank. The activating system also requires a solenoid which is rotatable. If three or more rocker arms are desired to be disabled the rocker arms from a practical standpoint will have to be along a straight line so that a common shaft can be extended therebetween.
U.S. patent application Ser. No. 09/537,648 Russ, et al., now U.S. Pat. No. 6,237,559, (commonly assigned) provides a four-cycle internal combustion engine with cylinder combustion chamber deactivation. The deactivated cylinder has an exhaust poppet valve which can be selectively disabled. In providing such an engine, it may be desirable over the course of engine life to alternate which cylinders are selectively disabled. Accordingly it is desirable to provide a partial or totally disabled rocker arm assembly which has a high speed response and which can easily be individualized for each rocker arm assembly. In the past it was thought that individual latch mechanism plungers could be readily disabled by a hydraulic system. Although the hydraulic system worked it has been found that the speed of hydraulic movement of the pin is not fast enough for the rocker arm assembly to have a response which allows for the optimum emission reduction characteristics for the engine.